An LTE system of which the specifications are formulated in 3GPP (3rd Generation Partnership Project), which is a project aiming to standardize a mobile communication system, supports downlink multi-antenna transmission (for example, see non patent document 1). For example, a base station can perform transmission with directing a beam toward one user terminal, and directing a null toward another user terminal.
In order to realize the downlink multi-antenna transmission in a FDD scheme, a user terminal feeds back precoder matrix information indicating a precoder matrix to a base station. Furthermore, the precoder matrix determines downlink transmission directionality.
Furthermore, in 3GPP, the standardization of coordinated transmission (CoMP; Coordinated Multi-Point) is in progress. In the CoMP, an antenna group (a base station) arranged in the same place is positioned as one “point” and a plurality of points communicate with a user terminal in coordination with one another. A point group that performs coordinated communication with a user terminal by using the same radio resource (time and frequency resource) is called a CoMP cooperating set.